Heretofore, there has been widely known various acrylate monomers such as methylacrylate, ethylacrylate, 2-ethylhexyl acrylate, etc., which are monofunctional monomers, and trimethylolpropane triacrylate, pentaerythritol triacrylate, etc., which are multifunctional monomers.
However, the monofunctional monomers have a disadvantage that an odor of the residual monomer after curing causes a remarkable problem in the case of using as a component of printing inks or coatings.
Furthermore, the multifunctional monomers also have a disadvantage that it is necessary to be used in large amounts to resins in the case of using as a diluent of printing inks or coatings, resulting in loss of excellent properties of the resins.
On the other hand, cyclohexyl methyl (meth)acrylate itself is readily polymerized or copolymerized with other compounds having unsaturated groups by heat, ultraviolet rays and or ionized radiations at the presence of an initiator for the radical polymerization.
In particular, an epoxidized cyclohexyl methyl (meth)acrylate which an alicyclic epoxy group capable of being cured by a cation, that is, 3,4epoxycyclohexyl methyl (meth)acrylate is useful for polymerizing or copolymerizing.
3,4-epoxycyclohexyl methyl (meth)acrylate is low in viscosity and mild in odor, and has the solubility to resins over a wide range, and further it is useful for inks, coatings, adhesives, covering agents and a raw material for molding resins or a modifier thereof.
It is noted that there have been basically known 3,4-epoxycyclohexyl methyl (meth)acrylate and a process for the preparation thereof, specifically by the esterification reaction of tetrahydrobenzyl alcohol with (meth)acrylic acid or by the transesterification reaction of tetrahydrobenzyl alcohol with a (meth)acrylate ester and successively by the epoxidation reaction with a peracid [Batog, A. E.; Zaitsev, S. Yu.; Kiryushima, N. P.; Zaitseva, V. V. (Inst. Fiz.-Org. Khim. Uglechim., Donetsk, USSR). Zh. Ors. Khim, 1982, 18(1), 90-4 (Russ)].
The reaction schemes are represented by the following formulae; ##STR1## [in the formulae, R.sup.1 is hydrogen or a methyl group, R.sup.2 is an alkyl group].
However, a process for the preparation of a purified, that is, a commercially available 3,4-epoxycyclohexyl methyl (meth)acrylate, has not been disclosed up to date.
In particular, there has not been known such a process that even a waste water treatment is taken into consideration or even a small amount of impurity detected by a heptane test described hereinafter can be removed.
On the other hand, it has been known that 3,4-epoxycyclohexyl methyl (meth)acrylate has a disadvantage of exceedingly readily polymerizing, particularly, through the preparation processes, while being stored and or shipped under the influence of heat, lights or other causes.
In order to solve the disadvantage, Japanese Patent Unexamined Publication (Kokai) No. 282,574/1990 teaches a method for preventing polymerization, which uses quinones, etc. together with phosphorous compounds under the presence of molecular state oxygen gas.
However, it has been found by the present inventors that the effect by the method described hereinabove in which the polymerization inhibitors are used is not sufficient in the case of preparation processes on a commercial basis.
It is one of reasons why the effect by the method was not sufficient that there was not able to anticipate sufficient qualities to be possessed in a product of 3,4-epoxycyclohexyl methyl (meth)acrylate, which was not produced on a commercial basis in those days when the Publication was filed.
Specifically describing, it requires that low boiling components in a commercially available 3,4-epoxycyclohexyl methyl (meth)acrylate must be removed to the extent of from 2 to 3%, more preferably, not more than 1%.
For that purpose, it requires that heating temperatures are raised and or that processing time of period is extended in the step of removing the low-boiling ingredients.
However, raising up of the temperatures or extension of processing time of period generates, even though minor amounts, the polymers in a product.
It has been found that the polymers in a product cause problems even though such minor amounts through the advanced developments in relation to a commercially available 3,4-epoxycyclohexyl methyl (meth)acrylate.
For example, it is one of the problems that the polymers ooze out as adhesive and insoluble substances in the case of preparing intermediate materials of resins for coatings using 3,4-epoxycyclohexyl methyl (meth)acrylate including the polymers, resulting in causing various problems through processing and in producing coatings having a remarkably spoiled commercial valuation.
It appears that the minor amounts of polymers in a commercially available 3,4-epoxycyclohexyl methyl (meth)acrylate are composed of the polymers of 3,4-epoxycyclohexyl methyl (meth)acrylate itself having a low molecular weight.
The contents of such polymers having a low molecular weight can be shown by weight % with a measuring method using n-heptane or n-hexane, in which 10 g of a product is dissolved in 100 cc of n-heptane or n-hexane and resulting suspensions are filtered and weighed (hereinafter, occasionally referred to as HT or HT value in a solubility test).
It is known that a commercially available 3,4-epoxycyclohexyl methyl (meth)acrylate must exhibit the HT value of not more than 0.1% by weight.
It was found that the method described in Japanese Patent Unexamined Publication (Kokai) No. 262594/1990 only can provide 3,4-epoxycyclohexyl methyl (meth)acrylate having the polymer contents of more than 0.1% by weight in HT value, more specifically, 0.14% by weight or so, which values are not sufficient in quality, by a recollected confirmation test using HT carried out thereafter.
That is, further more effective methods for inhibiting polymerizing in each step of the preparation processes must be developed in order to produce a purified 3,4-epoxycyclohexyl methyl (meth)acrylate on a commercial basis.
It is noted that 3,4-epoxycyclohexyl methyl (meth)acrylate has an alicyclic epoxy group which tends to exceedingly readily react with an organic acid derived from an organic peracid which is an epoxidation agent, for example, the epoxy group reacts with acetic acid derived from peracetic acid in the case of using peracetic acid as an organic peracid, resulting in polymerization of 3,4-epoxycyclohexyl methyl (meth)acrylate and opening of the epoxy group, particularly through an evaporation step.
Accordingly, it is required that the organic acid is removed from a crude reaction solution as early as possible in order to maintain a short time of period contacting with the epoxy group.
Such more effective methods do not have been developed up to date.
Furthermore, it is noted that, heretofore, various processes for removing the organic acid and organic peracid:
(a) a refining process by distillation;
In the case of a heat resistible product, this process has been usually carried out.
(b) a refining process by extraction with water;
The organic acid or organic peracid, which are dissolved in a crude reaction solution, is primarily removed by an extraction with water and successively by distillation, in order to prevent the polymerization or the side reaction of an epoxy compound on distilling the crude reaction solution without any refining processes.
(c) a refining process by neutralization; have been applied.
In the case of incapability of removing the organic acid or organic peracid or in the case that the organic acid in an aqueous solution readily reacts with an epoxy compound, this neutralization process has been usually applied.
Furthermore, in the case of incapability of removing the substances in which the polymerization and the side reaction are caused, by merely adjusting to neutralization point of PH of the solution, the substances are occasionally removed with an aqueous alkali solution.
Distillation is carried out in order to refine after removing the substances by neutralization.
However, the prior art (a) is often incapable of being applied, because it has a disadvantage that there are caused the polymerization or the opening reaction of epoxy groups by distillation alone because of easiness in the reaction of epoxy groups with an organic acid.
Furthermore, the prior arts (b) and (c), which are often applied in the case of incapability of applying the prior art (a), are also often incapable of being applied in the case of the rapid reaction velocity of epoxy groups with an organic acid.
Still further, the prior art (c) is often incapable of putting into practice on an industrial basis because of not only large amounts of a product loss but also a considerable load in water treatments.
As mentioned above, the prior arts (a), (b) and (c) include difficult disadvantages, respectively, in the case of applying on an industrial basis.
That is, the prior arts (a), (b) and (c) have been industrially incapable of being applied to an epoxy compound having properties that a crude reaction solution can not be refined by distillation alone because of the polymerization, the side reaction and that an epoxy group tends to rapidly react with an organic acid and or water.
A first aspect of the present invention relates to a method for reducing a contacting time of period between an organic solution layer and an aqueous solution layer on extracting an organic acid and an organic peracid with water from a crude reaction solution after the epoxidation reaction.
The first aspect has been found based on the mechanism in which the loss of an epoxidized product is caused by the reaction of the epoxidized product dissolved into water solution with water and an organic acid and a resultant concentration reduction of the epoxidized product and further repeatedly resultant dissolving, that is, by the form of a reaction-extraction which accelerates further dissolving into water.
A centrifugal extractor is essentially used and retention time of period therethrough is essentially adjusted within 5 minutes in the first aspect, whereby the reaction of an epoxy compound with an organic acid and water is not caused so much.
A second aspect of the present invention relates to a method for further removing small amounts of them by extracting an organic acid and organic peracid with water, and more specifically the method comprises neutralization with an alkali after separating with the apparatus as mentioned above.
It is noted that even though the centrifugal extractor as mentioned above is used in order to remove almost of the organic acid and organic peracid by extracting with water, there can not be removed small amounts of them.
And, there is a disadvantage in a product of 3,4-epoxycyclohexyl methyl (meth)acrylate refined by distillation in order to remove solvents and other low boiling components such as small amounts of starting materials after removing the organic peracid by extracting alone with water.
However, the neutralization before extracting the organic acid and organic peracid with water can not be applied on an industrial basis, from the view point of waste water treatments, which is described hereinabove.
The disadvantage in a product of 3,4-epoxycyclohexyl methyl(meth)acrylate is low in purity, for example, more specifically less than 90% in purity, and such unpurified 3,4-epoxycyclohexyl methyl (meth)acrylate undesirably has the tendency of readily polymerizing.
It is noted that there is required that the purity of the commercially available 3,4-epoxycyclohexyl methyl (meth)acrylate is from 94 to 97% by weight, and the residual components are primarily a starting material, a starting solvent and water.
From the above-described viewpoints, and as a result of studies by the present inventors, it has been found that a purified 3,4-epoxycyclohexyl methyl(meth)acrylate can be prepared by the various improved steps on a commercial basis.